History and Development of Astronomical Models and Physics

Vocabulary flashcards covering the historical evolution of cosmology, Aristotle's physics, Kepler's laws, Galileo's observations, and Newtonian mechanics.

Stellar Parallax

The apparent shift in the position of stars relative to each other that ancient Greeks reasoned they should see if the Earth moved through space, but were unable to observe.

Ptolemaic Model

An Earth-centered cosmological model in which the planets, Sun, and stars orbit the Earth, using epicycles to predict planetary phases and retrograde motion.

Epicycles

Smaller circular paths in the Ptolemaic model that loop around a main orbit (deferent), causing a planet to appear to move backwards from its original path to account for retrograde motion.

Natural Motion (Aristotelian)

Terrestrial motion determined by elements returning to their realms—heavy elements (earth and water) moving downward and light elements (fire and air) moving straight up—stopping once they arrive.

Forced Motion (Violent Motion)

Aristotelian motion that contradicts an object's preferred natural motion, such as horizontal motion or throwing a rock upwards, requiring constant external pushing or pulling.

Aether

The incorruptible element of the celestial realm whose natural motion is circular, uniform, and perfect, with no speeding up or slowing down.

Antiperistasis

Aristotle's explanation of projectile motion wherein an object pushes air aside, and the displaced air rushes to the back to propel the object forward until the violent motion expires and natural motion takes over.

12th Century Translation Movement

A historical movement that, alongside the rise of universities, helped reintroduce Greek scientific and astronomical knowledge to Western Europe after its preservation in monasteries.

Calendar Drift

An error of $11\,\text{minutes}$ a year caused by the Ptolemaic model, which left the calendar unaligned with the seasons and made it difficult to determine the date of Easter.

Copernican Model

A heliocentric model where the Sun is at the center and planets travel along perfectly round orbits with epicycles.

Tycho's Hybrid Model

A cosmological system where the Earth is stationary at the center, the Sun and Moon orbit the Earth, and all other planets orbit the Sun.

Tycho's Nova

A new celestial event observed by Tycho Brahe that contradicted the ancient Greek idea that the heavens were perfect and unchanging.

Kepler's First Law

The law stating that a planet's orbit is an ellipse with the Sun located at one of the foci points.

Kepler's Second Law

The law stating that a line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time, requiring the planet to travel faster when it is closer to the Sun.

Kepler's Third Law

The law stating that the square of a planet's orbital period ($P$) is directly proportional to the cube of the semi-major axis ($r$) of its orbit, represented as $P^2 = r^3$.

Phases of Venus

The full cycle of illuminated phases observed by Galileo using a telescope, which provided direct evidence that Venus orbits the Sun rather than the Earth.

Inferior Planet

A planet that is closer to the Sun than Earth is, exhibiting a full set of phases when viewed from Earth.

Superior Planet

A planet that is further from the Sun than Earth is, which does not display a full set of phases when viewed from Earth.

Galileo's Inclined Plane

An experimental apparatus used to slow down falling motion in order to measure time and distance more accurately.

Galileo's Double Inclined Plane

An experimental apparatus used to investigate the effects of friction by rolling balls down one ramp and observing how high they roll up the opposite side.

Newton's First Law of Motion

The law stating that an object remains at rest or stays in continuous motion until acted upon by an outside force.

Newton's Second Law of Motion

The physical law represented by $F = ma$, which applies to circular orbits through centripetal acceleration ($a_c = \frac{v^2}{r}$) and centripetal force ($F = \frac{m\,v^2}{r}$).

Newton's Third Law of Motion

The physical law stating that forces act in pairs.

Gravitational Acceleration

The constant rate of increasing speed at which all objects fall near Earth's surface, equal to $9.81\,\text{m/s}^2$.

Law of Universal Gravitation

Newton's synthesis of his laws of motion with Kepler's laws, demonstrating that the force pulling objects to Earth's ground is the exact same force pulling the Earth toward the Sun.

Newton's Mountain View of Orbits

The concept that orbital motion is achieved by launching a projectile horizontally from high above the atmosphere at sufficient velocity so that its trajectory curves around and continuously misses the Earth.

Apparent Weightlessness

The sensation of zero gravity experienced by an object when gravitational forces are still acting on it, but it remains in a state of continuous free fall.

Ocean Tides

Cyclical sea-level changes caused by the Moon's gravitational pull and the differences in that force, which become more extreme when the gravitational pull of the Sun aligns with that of the Moon.

Copernican Revolution

The fundamental shift that transformed science from a purely philosophical and observation-only discipline into an empirical, mathematical, and testable endeavor.